The present application relates to a non-aqueous electrolyte battery having enhanced input and output characteristics of a negative electrode and a negative electrode and to a method for manufacturing the same.
Among non-aqueous electrolyte batteries, a lithium ion secondary battery is rapidly developing as a power source of portable electronic devices such as a mobile phone and a personal computer. In the power source for such a portable electronic device, an energy density, namely an energy storage capacity per unit volume is the most necessary characteristic, and how long the portable electronic device can be used attracts interest. As to a negative electrode material of the lithium ion secondary battery, realization of a high density of the electrode using a carbon material of every sort has been developed. In all of the cases, it is aimed to enhance the energy density or cycle characteristics.
In the lithium ion secondary battery, when polyvinylidene fluoride with excellent lithium ion mobility is used as a negative electrode binder, input and output characteristics of the battery can be enhanced.
However, in discharging a more highly filled negative electrode at a larger current, there was involved a problem that since the lithium ion mobility in polyvinylidene fluoride is limited, polyvinylidene fluoride which covers the surface of a negative electrode active material impairs an interfacial reaction, and diffusion of lithium and electrochemical acceptance of lithium cannot keep up, whereby metallic lithium is easy to deposit on the negative electrode. In such a negative electrode, the metallic lithium deposited in the negative electrode is easily deactivated, resulting in an enormous lowering of cycle characteristics. Consequently, it has been difficult to increase the thickness of the active material layer or to increase the volume density.
Accordingly, for the purpose of obtaining a high-output battery, it is effective and important to reduce the ionic resistance in polyvinylidene fluoride.
As disclosed in JP-A-4-95363, when hexafluoropropylene is copolymerized with polyvinylidene fluoride, though the ionic resistance in the polyvinylidene fluoride can be reduced, the polyvinylidene fluoride itself is largely swollen in an electrolytic solution, and the electrode is swollen. Thus, favorable cycle characteristics cannot be secured.
Also, there is proposed a lithium ion secondary battery in which lithium diffusibility in a negative electrode is enhanced by mixing a ceramic particle in the negative electrode (see JP-A-10-255807). This intends to obtain a high-capacity lithium ion secondary battery by mixing a ceramic having high ionic conductivity in a negative electrode to enhance the diffusibility of a lithium ion, thereby reducing an internal resistance of the negative electrode. Also, it is possible to devise to enhance the strength of the electrode at the same time, and therefore, it becomes possible to enhance the cycle characteristics. It is described that it is possible to devise to enhance the battery performance by incorporating from 0.01 to 20 parts by weight of the ceramic based on 100 parts by weight of the negative electrode active material. At that time, a ceramic having a primary particle size of not more than 10 μm is used.